This invention relates, in general, to fabrication of optical devices and, more particularly, to interconnecting optical devices and optical fibers.
The coupling of an optical device or array of optical devices, an optical fiber or array of optical fibers, and an interconnecting substrate can be a difficult task. Usually the coupling is done manually or semi manually and can incur several problems such as being complex, inefficient, and not suitable for high volume manufacturing.
In order to reduce electrical parasitics, short electronic interconnects are needed between semiconductor photonic devices such as lasers and photodiodes and electronic interface circuitry. This electronic circuitry may include photonic signal drivers and photonic signal receivers. The need for decreased distance between photonic devices and electrical interface circuitry increases as the signaling data rate increases. Photonic components are often placed on simple carrier substrates to verify operation, to do bum-in, or simply to facilitate handling of that device. This photonic device and carrier substrate are then placed on another substrate and additional packaging is completed. This packaging adds additional electrical interfaces, such as wire bonds and long non-controlled impedance wires, decreasing the electrical performance of the photonic device.
In order to reduce optical losses and parasitics, efficient coupling of optical signals is needed. As optical signals tend to diverge from their original transmission axis, coupling devices or waveguides must be proximate optical transmitting and receiving devices. Signal loss increases with increased distances from an optical port to an optical connector, unless light is adequately directed through a coupling device. One example of a setup with limitations because of increased distance between the optical device and optical fiber is an electro-optic TO can with an optical port. After placing the optical component in a can and making electrical wire bonds, further packaging must be done in the alignment with a fiber optic cable. The distance between the optical device and the fiber is often relatively large, minimizing or eliminating the possibility of multiple optical devices on the same semiconductor substrate. With increased distances between a waveguide and multiple optical devices disposed on the same semiconductor, optical cross talk can reduce signal integrity.
Some prior art devices have reduced the length of electrical and/or optical interconnects by placing multiple components on a common, flexible substrate. Other prior art references teach of the use of lensing systems to guide light appropriately, thus allowing multiple optical devices on the same semiconductor while minimizing optical losses. Yet, lensing may require multiple optical couplings which can lead to signal loss. In addition, multiple waveguides require additional steps in aligning optical signals with an external optical waveguides and connectors, thus increasing manufacturing costs and decreasing yield.
Commonly used vertical cavity surface emitting laser (VCSEL) structures and photodiode structures have both electrical contacts and optical ports on the same surface of the semiconductor, creating packaging problems when trying to optimize the performance of each of these interfaces. These packaging problems are exacerbated when the optical components have arrays of optical devices. A novel packaging technique is described below under illustrated embodiments of the invention that combines complex electrical and optical trace patterns, and simplifies packaging by using a common transparent substrate. This transparent photonic circuit board could support arrays of photonic chips and electrical interface circuitry while reducing electrical losses, optical losses, and manufacturing costs.
A method and apparatus are provided for providing an electro-optic signal processing device. The method includes the steps of providing an optically transparent substrate having first and second planar elements with an abutting common edge, the planar elements lying at differing angles with respect to each other about the common edge and a plurality of alignment apertures formed in the substrate. A plurality of optical devices of an optical array are disposed on the first planar element of the substrate, with transmission paths of the optical devices passing directly through the substrate. A signal processor is also disposed on the first planar element of the substrate. An optical fiber holder comprising a plurality of respective optical fibers and guide pin apertures disposed on a first surface of the optical fiber holder is aligned to the optical array using the guide pins and guide pin apertures. Optical signals of the optical devices of the optical array are coupled to respective optical fibers of the aligned optical fiber holder. A printed circuit board having a first surface is attached to a mating surface of the substrate""s second planar element.